Identifying and preventing the carrot fly
The carrot fly is the most important pest of carrots – and unfortunately one you only notice at harvest. It is not the small, glossy-black fly itself that does the damage, but its maggots: they bore into the roots and leave rusty-brown feeding tunnels. Besides carrots, celery, parsley and parsnip are also affected.
Because control in the soil is hardly possible, prevention is the focus here too. The good news: with the right measures the carrot fly can be kept away very reliably.
In short
- The maggots eat rusty-brown tunnels into the roots – the carrots turn bitter.
- First signs: reddish, wilting foliage.
- The fly flies low and is attracted by the carrot scent (especially when thinning).
- Best remedy: an insect-proof net from sowing onwards.
How to spot an infestation
Above ground, an infestation shows through reddish to bronze-coloured, wilting foliage. When you pull up the roots, the typical rusty-brown, corky feeding tunnels appear, in which the pale, legless maggots sit. Heavily affected carrots taste bitter and rot quickly in storage.
The life cycle of the carrot fly
The carrot fly produces two to three generations a year – the first flies from about May, another in late summer. The females are attracted over long distances by the scent of carrots, especially when plant sap is released during thinning. They lay their eggs on the ground next to the plants.
Preventing the carrot fly
- Insect-proof net: lay a fine-meshed net directly after sowing – the most reliable method.
- Sow thinly: so less thinning is needed; if you do thin, do it late in the evening in calm weather when the flies are inactive, and remove the thinnings immediately.
- Mixed culture: onions, leeks or garlic between the carrot rows – their scent masks the carrot smell.
- Choose the sowing time: very early or from mid-May/June onwards avoids the main flight period.
- Barrier: the fly flies low (below about 50–60 cm) – a fine-meshed fence around the bed keeps it out.
- Crop rotation: do not grow carrots in the same spot year after year.
What to do in case of infestation
- Sort out affected carrots and do not store them.
- Harvest early: in the case of a late-summer infestation, harvest the carrots promptly before the second generation strikes.
- Loosen the soil & rotate: change the spot the following year to break the cycle.
Tip
Never thin carrots on a warm, sunny day – the intense scent attracts the flies. Late evening under a cloudy sky is ideal.
Caution
A net only helps if it closes tightly all round and the crop rotation is right – if old, infested roots remain in the same bed, the flies hatch right underneath it.
Frequently asked questions
Can I still eat affected carrots?
Lightly affected carrots can be cut out generously; heavily bored and rotten ones are better discarded.
Does mixed culture with onions really help?
It noticeably reduces the infestation, but under heavy pressure it does not replace a net – best to combine both.
Strong young plants and healthy seed lay the foundation for aromatic, healthy carrots. In our nursery we focus on robust quality.